A casting has unnecessary portions to be removed such as a pouring gate, a weir, burr and so forth. These unnecessary portions are removed in the finishing process. In order to remove these unnecessary portions, it is conventional to conduct punching on these portions with a hydraulic press or mechanical press to which a cutting blade is attached. Concerning the excess metal of a casting, there are two types. One is the excess metal of a casting which is unavoidably generated in the process of casting, and the other is the excess metal of a casting which is intentionally provided for accomplishing a predetermined design object. Therefore, the latter can not be necessarily defined as an unnecessary portion of a casting. However, in the present invention, irrespective of the cause of the generation of the excess metal of a casting, portions, which must be removed from the casting after the completion of the casting process, are defined as the excess metal of the casting. In general, the larger the volumes of the excess metal portions are, the more difficult it becomes to remove the excess metal portions from the casting.
Concerning the prior art, the object of which is to remove the excess metal from a casting, for example, JP-A-2004-17127 discloses a deburring apparatus and burr blanking tool used therefore. According to the invention disclosed in JP-A-2004-17127, an annular burr portion generated in the peripheral edge of an insulator cap, which is a casting manufactured by a split mold, is removed by means of punching. In this case, an annular punching blade is used which is composed of high and low blades, the heights of the blade ends are different from each other in the punching direction. The high blades are separate from each other at predetermined intervals, and the low blades are arranged between the high blades. Therefore, at first, a work is punched out by the high blades in such a manner that the punched portions are formed like dotted lines. Successively, the low blades punch out portions between the dotted lines. Due to the foregoing, it is possible to reduce the maximum shearing load necessary for annular cutting.
According to the above invention in which the burr is cut off by the high and low blades, the following effects are expected. Since the entire circumference is not cut at the same time, as compared with a conventional case in which cutting is conducted with a conventional annular cutting blade, the maximum cutting load can be reduced to about 30%. However, in the above invention, the prior cutting is conducted with the high blades, and the successive cutting is conducted with the low blades. Therefore, any portion of the burr is subjected to the cutting action only once. Accordingly, this method is effectively used for removing the burr, the volume of which is relatively small. However, this method is not effectively used for removing an excess metal portion of a casting such as a portion of the casting which is provided for the design object, the volume of which is relatively large.
JP-A-11-197820 discloses a method of removing an unnecessary portion from a casting. According to this invention, similar blade faces, which are arranged in an upper and a lower blade, are composed in such a manner that the similar blade faces are formed into shapes similar to the cutting portion of a casting. When the upper and the lower blades slide to and bite into a portion to be cut, the unnecessary portion of the casting is cut off. Since the upper and the lower blade have similar blade faces, the upper and the lower blade are fitted to the outer shape of the cutting portion. Accordingly, the upper and the lower blade smoothly bite into the cutting portion without fluctuation. Since the upper and the lower blade have shoulder blades at the respective blade ends, no cracks are caused in the cutting portion. Therefore, it is expected that the cutting can be beautifully conducted. In this case, the similar blade faces provided in the upper and the lower blade are similar to the cutting portion of the casting. Therefore, it can be considered that cutting is conducted to be a shape which is similar to the cutting portion. Accordingly, it is estimated that this work is similar to a deburring work. Therefore, it is unknown whether or not the capacity of removing an unnecessary portion from a casting, the volume of which is relatively large, is sufficiently large.
On the other hand, the main object of the present invention is to remove an excess metal portion from a casting in the process of working the casting, that is, the main object of the present invention is to remove an excess metal portion from a casting which is necessary from the viewpoint of designing the casting. For example, in the bracket of the disk brake for automobile use shown in FIGS. 11 and 12, the casting 1 requires the brake pad guides 4 in which both end pieces 3, 3 of the brake pad 2 are arranged. It is an object of the present invention to form the brake pad guides 4 by executing the method of removing the excess metal from the casting. The portion 5, in which the brake pad guide 4 is formed, can not be formed into a recess shape because of the restriction of the casting mold. Therefore, the portion 5 must be left as the excess metal of the casting 1 having the leaves shown in FIG. 11. In this connection, reference numeral 6 is a caliper. In order to form the brake pad guide 4, it is necessary to form a recess portion in the excess metal portion 5. Compared with the conventional method in which only one side of a protruding root portion is cut off, it is necessary to cut off three sides. Therefore, the cutting resistance is three times as high as that of the conventional method. Actually, a higher intensity of the cutting force is required. Accordingly, an excessively heavy load is given to the blade. Therefore, it seems to be difficult that the cutting is conducted by a press. A recess portion such as a brake pad guide can not be formed by means of cutting off but it is common that a recess portion such as a brake pad guide is formed with a machine tool. However, when the machine tool is used, the man-hour is increased and the manufacturing cost is raised. Further, when a new machine tool is used for finishing a casting, an excessive equipment investment is required.
[Patent Document 1] JP-A-2004-17127
[Patent Document 2] JP-A-11-197820